Correlating Label Switched Paths Of A Pseudowire

ABSTRACT

In one embodiment, correlating label switched paths of a pseudowire includes receiving a first message at a second label switching router. The first message is sent from a first label switching router and includes a pseudowire identifier and a first label switched path identifier. The pseudowire identifier identifies a pseudowire, and the first label switched path identifier identifies a first label switched path that implements the pseudowire. A second message is sent from the second label switching router to the first label switching router. The second message comprises the pseudowire identifier and a second label switched path identifier. The second label switched path identifier identifies a second label switched path that implements the pseudowire.

TECHNICAL FIELD

This invention relates generally to the field of communication networksand more specifically to correlating label switched paths of apseudowire.

BACKGROUND

A pseudowire (PW) is an emulation of a native service over a PacketSwitched Network (PSN). The pseudowire emulates the operation of atransparent wire that carries the native service, and may be used tocarry packets from a network that uses the native service, across aPacket Switched Network, to another network that uses the nativeservice.

SUMMARY OF THE DISCLOSURE

In accordance with the present invention, disadvantages and problemsassociated with previous techniques for using pseudowires may be reducedor eliminated.

According to one embodiment of the present invention, correlating labelswitched paths of a pseudowire includes receiving a first message at asecond label switching router. The first message is sent from a firstlabel switching router and includes a pseudowire identifier and a firstlabel switched path identifier. The pseudowire identifier identifies apseudowire, and the first label switched path identifier identifies afirst label switched path that implements the pseudowire. A secondmessage is sent from the second label switching router to the firstlabel switching router. The second message comprises the pseudowireidentifier and a second label switched path identifier. The second labelswitched path identifier identifies a second label switched path thatimplements the pseudowire.

Certain embodiments of the invention may provide one or more technicaladvantages. A technical advantage of one embodiment may be that amessage includes a pseudowire-to-label switched path (PW-to-LSP) mappingthat maps a pseudowire to paths that implement the pseudowire. Themessage is sent to nodes of the pseudowire to the inform the nodes ofthe paths that implement the pseudowire. If one node detects a fault onone path, the node may use the other path to send a failure notificationto the other node.

Certain embodiments of the invention may include none, some, or all ofthe above technical advantages. One or more other technical advantagesmay be readily apparent to one skilled in the art from the figures,descriptions, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsfeatures and advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates an example of a system for correlating label switchedpaths of a pseudowire;

FIG. 2 illustrates an example of a pseudowire implemented by paths ofthe system of FIG. 1; and

FIG. 3 illustrates an example of a method for correlating label switchedpaths of a pseudowire.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention and its advantages are bestunderstood by referring to FIGS. 1 through 3 of the drawings, likenumerals being used for like and corresponding parts of the variousdrawings.

FIG. 1 illustrates a system 10 for correlating label switched paths of apseudowire. In the embodiment, a pseudowire 14 that includes nodes 24 isimplemented by paths 20, such as label switched paths. A message 30includes a pseudowire-to-label switched path (PW-to-LSP) mapping thatmaps pseudowire 14 to paths 20. Message 30 is sent to nodes 24 to informnodes 24 of paths 20 that implement pseudowire 14. A node 24 may use apath 20 to send a notification, such as a failure notification, toanother node 24.

In one embodiment, system 10 communicates information through signalssuch as optical signals (for example, Synchronous Transport Signals(STSs)). As an example, an optical signal may have a data rate of 10,20, 40, or over 40 gigabits per second. Information may include voice,data, audio, video, multimedia, control, signaling, and/or otherinformation.

In the illustrated embodiment, system 10 includes Layer 1 or Layer 2(Layer 1/2) networks 16 (networks 16 a and 16 b) and a packet switchednetwork (PSN) 18. Layer 1/2 network 16 uses a native service thatimplements Layer 1/2 protocols, such as Asynchronous Transfer Mode(ATM), Frame Relay, Ethernet, Time-Division Multiplexing (TDM),synchronous optical networking/synchronous digital hierarchy(SONET/SDH), and/or other suitable Layer 1/2 protocols. Layer 1/2networks 16 a and 16 b include clients 22 a and 22 c. A client 22communicates using Layer 1/2 protocols.

Packet switched network (PSN) 18 implements Layer 3 or higher protocolssuch as MultiProtocol Label Switching (MPLS), Internet Protocol (IP), orLayer 2 Tunneling Protocol (L2TP). Packet switched network 18 includesnodes 24 a, 24 b, and 24 c. Node 24 represents any suitable networkelement such as a Multi-Protocol Label Switching (MPLS) MPLS router, orlabel switching router.

A path 20, or circuit or tunnel, comprises a sequence of nodes 24 thatcommunicate packets. Path 20 may be a label switched path (LSP). Packetstravel from an ingress node 24 a, through zero, one, or moreintermediate nodes 24 b, to an egress node 24 c. In the illustratedexample, path 20 a goes from ingress node 24 a through intermediate node24 b to egress node 24 c. Path 20 b goes from ingress node 24 c throughintermediate node 24 b to egress node 24 a. A path identifier identifiespath 20. In the illustrated example, path identifier LSP₁ identifiespath 20 a, and path identifier LSP₂ identifies path 20 b. A node 24 maymanage the pseudowire parameters, such as the pseudowire identifiers andlabels, as well as the source, destination, and path identifiers.

To route a packet along path 20 a, ingress node 24 a attaches a label toa packet and sends the packet to a next hop node according to aforwarding entry for path 20 a. Intermediate node 24 b uses the labelfrom node 24 a to look up another forwarding entry. Intermediate node 24b replaces the label from node 24 a with a new label and sends thepacket to a next hop node according to the forwarding entry. Egress node24 c uses the label from node 24 b to look up a forwarding entry. Theforwarding entry indicates that node 24 c is the egress node.

Pseudowire 14 is implemented by paths 20 a and 20 b. Pseudowire 14emulates Layer 1/2 services over packet switched network 18, and allowsfor Layer 1/2 packets to be communicated over packet switched network18. Pseudowire acts like a Layer 1/2 wire and may be used to forwardLayer 1/2 packets from one Layer 1/2 network 16 a to another Layer 1/2network 16 b over packet switched network 18.

A particular pseudowire 14 may be used to communicate packets toparticular clients. For example, pseudowire 14 a communicates betweenclients 22 a, and pseudowire 14 b communicates between clients 22 b.

A pseudowire identifier identifies a particular pseudowire 14. Forexample, pseudowire identifier PW₁ identifies pseudowire 14 a, andpseudowire identifier PW₂ identifies pseudowire 14 b. Pseudowire labelsare allocated to a particular pseudowire 14 during setup of thepseudowire 14. In one embodiment, one label PWL₁ may be given to apseudowire PW₁ in one direction, and another label PWL₂ may be given tothe same pseudowire PW₁ in the other direction.

Message 30 communicates information about pseudowire 14 to nodes 24 ofpath 20. In the illustrated embodiment, message 30 includes apseudowire-to-label switched path (PW-to-LSP) mapping 34. PW-to-LSPmapping 34 indicates paths 20 that implement pseudowire 14. PW-to-LSPmapping 34 includes a pseudowire identifier 36, a pseudowire label 38,and a label switched path identifier 42.

In the illustrated embodiment, node 24 a sends message 30 a to node 24c, and node 24 c sends message 30 b to node 24 a. PW-to-LSP mapping 34 ainforms node 24 c of path 20 a that implements pseudowire 14 a, andPW-to-LSP mapping 34 b informs node 24 a of path 20 b that implementspseudowire 14 a.

Specifically, pseudowire identifier 36 a includes pseudowire identifierPW₁ identifying pseudowire 14 a, pseudowire label 38 a includes labelPWL₁ identifying pseudowire 14 a in one direction, and label switchedpath identifier 42 a includes path identifier LSP₁ identifying path 20a. Pseudowire identifier 36 b includes pseudowire identifier PW₁identifying pseudowire 14 a, pseudowire label 38 b includes label PWL₂identifying pseudowire 14 a in the other direction, and label switchedpath identifier 42 b includes path identifier LSP₂ identifying path 20b.

Message 30 represents any suitable message, for example, a LabelDistribution Protocol (LDP) a label mapping message used to set up apseudowire 14 or an LDP notification message used to update pseudowire14. PW-to-LSP mapping 34 may be communicated in any suitable portion ofmessage 30, for example, a type-length-value (TLV) element.

PW-to-LSP mapping 34 allows ingress and egress nodes 24 a and 24 c toknow paths 20 used to form pseudowires 14. Accordingly, in the eventthat a path 20 a of a pseudowire 14 fails, egress node 24 c can notifyingress node 24 a using the other path 20 b. Using the other path 20 bmay be more efficient since path 20 b does not require IP forwarding.

A component of system 10 may include an interface, logic, memory, and/orother suitable element. An interface receives input, sends output,processes the input and/or output, and/or performs other suitableoperation. An interface may comprise hardware and/or software.

Logic performs the operations of the component, for example, executesinstructions to generate output from input. Logic may include hardware,software, and/or other logic, and may be embodied as a computer-readablestorage medium. Certain logic, such as a processor, may manage theoperation of a component. Examples of a processor include one or morecomputers, one or more microprocessors, one or more applications, and/orother logic.

A memory stores information. A memory may comprise computer memory (forexample, Random Access Memory (RAM) or Read Only Memory (ROM)), massstorage media (for example, a hard disk), removable storage media (forexample, a Compact Disk (CD) or a Digital Video Disk (DVD)), databaseand/or network storage (for example, a server), and/or othercomputer-readable medium.

Modifications, additions, or omissions may be made to system 10 withoutdeparting from the scope of the invention. The components of networksystem 10 may be integrated or separated according to particular needs.Moreover, the operations of network system 10 may be performed by more,fewer, or other devices. Additionally, operations of network system 10may be performed using any suitable logic. As used in this document,“each” refers to each member of a set or each member of a subset of aset.

FIG. 2 illustrates an example of pseudowire 14 implemented by paths 20 aand 20 b of system 10 of FIG. 1. Pseudowire 14 communicates data traffic54 and bidirectional forwarding detection (BFD) control packets 58.Bidirectional forwarding detection detects a data plane failure in theforward path of a label switched path 20. To detect a data plane failureof path 20 a, ingress node 24 a sends one or more failure detectionpackets to egress node 24 c over path 20 a. The failure detectionpackets may be BFD control packets that are sent at a configurable rate.

If egress node 24 c does not receive the packets in an expected manner,path 20 a is declared to be faulty. An unexpected manner indicatingfailure may occur if, for example, the packets do not have the expectedcontents, a particular number of packets fails to arrive, and/or thepackets are late. Egress node 24 c sends a failure notification on path20 b indicating that there is a failure of path 20 a.

FIG. 3 illustrates one embodiment of a method for correlating labelswitched paths of a pseudowire. According to one embodiment, the methodmay be performed by system 10.

Steps 110 through 126 describes setup of path 20 a according to, forexample, Resource Reservation Protocol (RSVP). Node 24 a initiates setupof path 20 a from node 24 a to node 24 c at step 110. Node 24 adetermines that path 20 a includes node 24 a, node 20 b, and node 24 c.A BFD instance is allocated. Node 24 a sends a reservation request tonode 24 b at step 114. Node 24 b processes the reservation request, andforwards the reservation request to node 24 c at step 118.

Node 24 c selects label L₂ for the link from node 24 c to node 24 b, andsends the label L₂ to node 24 b in a reservation response at step 122.Node 24 b selects a label L₁ for the link from node 24 b to node 24 a,and sends the label L₁ to node 24 a in a reservation response at step126.

Steps 130 through 146 describe setup of path 20 b from node 24 c to node24 a. Node 24 c initiates setup of path 20 b from node 24 c to node 24 aat step 130. Node 24 c determines that path 20 b includes node 24 c,node 20 b, and node 24 a. A BFD instance is allocated. Node 24 c sends areservation request to node 24 b at step 134. Node 24 b processes thereservation request, and forwards the reservation request to node 24 aat step 138.

Node 24 a selects label L₃ for the link from node 24 a to node 24 b, andsends the label L₃ to node 24 b in a reservation response at step 142.Node 24 b selects a label L₄ for the link from node 24 b to node 24 c,and sends the label L₄ to node 24 c in a reservation response at step146.

Steps 150 and 154 describe setup of pseudowire PW₁ according to, forexample, LDP. The setup involves notification of nodes 24 a and 24 c ofpaths LSP₁ and LSP₂ that implement pseudowire PW₁. The notification mayalso be performed during an update process. Node 24 a sends PW-to-LSPmapping 34 a to node 24 c at step 150. Node 24 a selects path LSP₁ forpseudowire PW₁. In the illustrated embodiment, PW-to-LSP mapping 34 aincludes pseudowire identifier PW₁, pseudowire label PWL₁, and LSPidentifier LSP₁.

Node 24 c sends PW-to-LSP mapping 34 b to node 24 a at step 154. Node 24c selects path LSP₂ for pseudowire PW₁. PW-to-LSP mapping 34 b includespseudowire identifier PW₁, pseudowire label PWL₂, and LSP identifierLSP₂.

Steps 160 through 172 describe communication of data between nodes 24 aand 24 c. Node 24 a sends data packets designated for clients C₁ to node24 b at step 160. The data packets include pseudowire label PWL₁ andlabel L₁. Node 24 b sends data packets to node 24 c at step 164. Thedata packets include pseudowire label PWL₁ and label L₂. Node 24 cremoves the labels and forwards the packets to client C₁. Node 24 csends data packets to node 24 b at step 168, and node 24 b sends thedata packets to node 24 a at step 172.

Steps 174 through 188 describe performance of bidirectional forwardingdetection. The BFD instance is configured at step 174 with transmit andreceive labels that allow the BFD detection packets and failurenotifications to travel over paths 20 a and 20 b.

Node 24 a sends one or more BFD detection packets to node 24 c alongpath 20 a at steps 180 and 182. Node 24 c detects a failure at step 184.Node 24 c sends a BFD failure notification along path 20 b at steps 186and 188. The failure notification indicates that a failure of path 20 ahas been detected.

Certain embodiments of the invention may provide one or more technicaladvantages. A technical advantage of one embodiment may be that amessage includes a pseudowire-to-label switched path (PW-to-LSP) mappingthat maps a pseudowire to paths that implement the pseudowire. Themessage is sent to nodes of the pseudowire to the inform the node of thepaths that implement the pseudowire. A node may use a path to send anotification, such as a failure notification, to another node.

While this disclosure has been described in terms of certain embodimentsand generally associated methods, alterations and permutations of theembodiments and methods will be apparent to those skilled in the art.Accordingly, the above description of example embodiments does notconstrain this disclosure. Other changes, substitutions, and alterationsare also possible without departing from the spirit and scope of thisdisclosure, as defined by the following claims.

1. A method for correlating a plurality of label switched paths of apseudowire, comprising: receiving a first message at a second labelswitching router, the first message sent from a first label switchingrouter, the first message comprising a pseudowire identifier and a firstlabel switched path identifier, the pseudowire identifier identifying apseudowire, the first label switched path identifier identifying a firstlabel switched path that implements the pseudowire; and sending a secondmessage from the second label switching router to the first labelswitching router, the second message comprising the pseudowireidentifier and a second label switched path identifier, the second labelswitched path identifier identifying a second label switched path thatimplements the pseudowire.
 2. The method of claim 1, wherein: the firstmessage comprises a first label mapping message; and the second messagecomprises a second label mapping message.
 3. The method of claim 1,wherein: the first message comprises a first label updating message. 4.The method of claim 1, further comprising: detecting, by the secondlabel switching router, a failure of the first label switched path usingbi-directional forwarding detection.
 5. The method of claim 1, furthercomprising: detecting a failure of the first label switched path; andsending a notification of the failure from the second label switchingrouter to the first label switching router along the second labelswitched path.
 6. The method of claim 1, further comprising: expectingone or more failure detection packets from the first label switchingrouter, the one or more failure detection packets sent from the firstlabel switching router along the first label switched path; anddetecting a failure of the first label switched path in accordance withthe expectation.
 7. The method of claim 1, the pseudowire operable tocommunicate data traffic and detection control traffic between the firstlabel switching router and the second label switching router.
 8. Asystem for correlating a plurality of label switched paths of apseudowire, comprising: an interface of a second label switching router,the interface operable to: receive a first message sent from a firstlabel switching router, the first message comprising a pseudowireidentifier and a first label switched path identifier, the pseudowireidentifier identifying a pseudowire, the first label switched pathidentifier identifying a first label switched path that implements thepseudowire; and one or more processors operable to: generate a secondmessage comprising the pseudowire identifier and a second label switchedpath identifier, the second label switched path identifier identifying asecond label switched path that implements the pseudowire; the interfacefurther operable to: send the second message to the first labelswitching router.
 9. The system of claim 8, wherein: the first messagecomprises a first label mapping message; and the second messagecomprises a second label mapping message.
 10. The system of claim 8,wherein: the first message comprises a first label updating message. 11.The system of claim 8, the one or more processors further operable to:detect a failure of the first label switched path using bi-directionalforwarding detection.
 12. The system of claim 8, the one or moreprocessors further operable to: detect a failure of the first labelswitched path; and send a notification of the failure to the first labelswitching router along the second label switched path.
 13. The system ofclaim 8, the one or more processors further operable to: expect one ormore failure detection packets from the first label switching router,the one or more failure detection packets sent from the first labelswitching router along the first label switched path; and detect afailure of the first label switched path in accordance with theexpectation.
 14. The system of claim 8, the pseudowire operable tocommunicate data traffic and detection control traffic between the firstlabel switching router and the second label switching router.
 15. Logicfor correlating a plurality of label switched paths of a pseudowire, thelogic embodied in a computer-readable storage medium and operable to:receive a first message at a second label switching router, the firstmessage sent from a first label switching router, the first messagecomprising a pseudowire identifier and a first label switched pathidentifier, the pseudowire identifier identifying a pseudowire, thefirst label switched path identifier identifying a first label switchedpath that implements the pseudowire; and send a second message from thesecond label switching router to the first label switching router, thesecond message comprising the pseudowire identifier and a second labelswitched path identifier, the second label switched path identifieridentifying a second label switched path that implements the pseudowire.16. The logic of claim 15, wherein: the first message comprises a firstlabel mapping message; and the second message comprises a second labelmapping message.
 17. The logic of claim 15, wherein: the first messagecomprises a first label updating message.
 18. The logic of claim 15,further comprising: detecting a failure of the first label switchedpath; and sending a notification of the failure from the second labelswitching router to the first label switching router along the secondlabel switched path.
 19. The logic of claim 15, the pseudowire operableto communicate data traffic and detection control traffic between thefirst label switching router and the second label switching router. 20.A system for correlating a plurality of label switched paths of apseudowire, comprising: means for receiving a first message at a secondlabel switching router, the first message sent from a first labelswitching router, the first message comprising a pseudowire identifierand a first label switched path identifier, the pseudowire identifieridentifying a pseudowire, the first label switched path identifieridentifying a first label switched path that implements the pseudowire;and means for sending a second message from the second label switchingrouter to the first label switching router, the second messagecomprising the pseudowire identifier and a second label switched pathidentifier, the second label switched path identifier identifying asecond label switched path that implements the pseudowire.